Hard-metal body

ABSTRACT

The invention relates to a hard-metal body whose hard-metal phase consist of tungsten carbide and whose binder metal phase consists of nickel and chrome. 
     Especially for the enhancement of the corrosion resistance it is proposed that the hard metal contain also TiN in addition to the hard-metal phase, whereby the content of TiN and and binder metal phase amounts to 5 to 25% by mass and is composed by 0.1 to 10% by mass TiN, 5 to 15% by mass chrome, the balance being made up by nickel.

The invention relates to a hard-metal body according to the introductorypart of claim 1.

Such hard metals are already known, e.g. the European patentspecification EP 0 195 965 A3 discloses a hard metal, which besides thehard-metal phase contains binder metal phase between 5 to 25% by weight,which is composed by 5 to 15% by weight chrome and the balance nickel,and whereby after sintering, the hard metal is treated for a period of20 to 200 minutes in an atmosphere of inert gas, preferably an argonatmosphere, at a temperature of 1300° to 1400° C. and a pressure of 20to 3000 bar.

The U.S. Pat. No. 3,215,510 discloses a hard-metal body consisting of 10to 30% by mass of a chrome-nickel binder alloy, the balance made up bytungsten carbide, whereby the weight ratio of chrome to the binder metalranges between 0.015 and 0.15. This hard-metal body is produced bypressing and sintering from powdery raw materials.

Finally the JP-A-56 136 952 presents a sintered hard-metal body on thebasis of WC-Ni, which contains 3 to 30% Ni and 0.05 to 4.5% Cr, as wellas 0.5 to 20% of at least one nitride of Ti, Zr, V, Nb. Further, in theGerman article by Kieffer and Benesowsky, in HARTMETALLE, 1965, pages220, 221 and 228, a hard metal is described consisting of 90% by masstungsten carbide, 8% by mass nickel and 2% by mass chrome. However,these in themselves corrosion-resistant hard metals havedisadvantageously a very low strength and especially a very lowductility, so that their practical applications are limited.

From EP 0 028 620 B1 a further sintered hard alloy is known, which forthe purpose of achieving good strength, ductility, as well as corrosionand oxidation resistance, consists of 55 by 95% by volume of hardmaterials with a minimum of 90% tungsten carbide and optionally furthercarbides, as well as 5 to 45% by volume single-phase binders with aminimum of 50% nickel, 2 to 25% chrome, 1 to 15% molybdenum and as amaximum for each 10% manganese, 5% aluminum, 5% silicon, 10% copper, 30%cobalt, 20% iron and 13% tungsten.

Finally, in EP 0 214 679 A1 a corrosion-resistant hard-metal alloy isproposed consisting of 31 to 84% by weight tungsten carbide, 15 to 60%by weight of one or several carbides of the group tantalum carbide,niobium carbide, zirconium carbide, titanium carbide, chrome carbide,molybdenum carbide,as well as 1 to 9% by weight of a binder alloy ofnickel and/or cobalt with a 2 to 40% by weight chrome addition. Thisalloy is also supposed to have good mechanical strength characteristicsand a high resistance to wear.

Experience has proven that the heretofore-known alloys are notsatisfactory from the point of view of corrosion resistance.

It is therefore the object of the present invention to propose ahard-metal body having high mechanical strength as well as wearresistance, and in addition thereto, an improved resistance tocorrosion.

This object is attained due to the hard-metal body defined in claim 1,consisting of tungsten carbide, 0.005 to 0.3% by mass TiN, chrome andnickel, whereby the proportion of TiN and binder metal phase togetheramounts to 5 to 25% by mass, and this proportion contains 5 to 15% bymass chrome and which is produced from powdery raw materials throughpressing and sintering. The advantages of this alloy are an improvedcorrosion resistance, particularly in the medium sulfuric acid, and thesimultaneous considerable reduction of abrasion wear. The goodmechanical characteristics make possible a safe use of the alloy inchemical plants, as well materials exposed to extreme combustiontemperatures.

According to a further embodiment of the invention, after sintering thehard-metal body is treated during 20 to 200 minutes in an atmosphere ofinert gas, particularly argon atmosphere, at a temperature of 1300° to1400° C. and at a pressure of 20 to 3000 bar. As a result of thistreatment, the hard metal achieves a good strength and an excellentductility, which can be explained by a high degree of densification ofthe hard-metal structure. Especially, it is possible to cool down thesintered hard-metal body and then to treat it in a separate installationat 100 to 3000 bar or immediately after sintering in the sintering plantat 20 to 100 bar. This shows that the immediate treatment aftersintering allows operation at low pressures.

Preferably, in the hard-metal body according to the invention 1 to 30%by mass of the tungsten carbide is replaced by titanium carbide,tantalum carbide and/or niobium carbide.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are graphs illustrating the examples.

In a special embodiment example, three alloys, which have been subjectedto the same treatment steps are compared to each other. In all cases,the start was a powdery mix of raw materials with a particle size of 0.5to 5 μm. The pressing and sintering of the hard metal was performedaccording to the state of the art in the known manner at approximately1400° C. The composition in % by mass results from the following table:

Material 1: 90.5% by mass WC, 8.5% Ni, 1% Cr

Material 2: 90.2% by mass WC, 8.5% Ni, 1% Cr, 0.3% Mo

Material 3: 90.2% by mass WC, 8.5% Ni, 1% Cr, 0.3% TiN

The finished sintered metals subsequently subjected to an inert-gasatmosphere under pressure showed the specific mass loss illustrated inFIG. 1: the abrasion wear of the hard-metal body of the invention wasthereby clearly lower than the one of the two other materials 1 and 2known to the state of the art.

The solutions had the following compositions: H₂ O with 300 mg Cl^(-b)/1 and 200 mg SO₄ ⁻⁻ /1 as sodium salts with acetic acid set to a pH=4.The thereby measured current-density/potential curves are shown in FIG.2. In the established test conditions, the hard metal with theTiN-addition according to the invention shows a current surge only atmore positive potentials, proving this way a lower sensitivity tocorrosion.

I claim:
 1. Sintered hard-metal body, consisting of tungsten carbide,0.005 to 0.3% by mass TiN, and metal binder of phase of chrome, andnickel, whereby the content of TiN and metal binder phase togetheramounts to 5 to 25% by mass, this content comprising 15% by mass chrome,and which has been produced from powdery raw materials through pressingand sintering.
 2. Hard-metal body according to claim 1, wherein aftersintering the hard metal is treated during a time period of 20 to 200minutes in an atmosphere of inert gas, preferably argon, at atemperature of 1300° to 1400° C. and a pressure of 20 to 3000 bar. 3.Hard metal according to claim 1 wherein 1 to 30% by mass of the tungstencarbide is replaced by titanium carbide, tantalum carbide and/or niobiumcarbide.